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Dietary ractopamine increases lean tissue deposition, with the responses most evident at ad libitum feed intakes whereas dietary betaine can improve growth by reducing maintenance requirements, with the greatest responses occurring when energy is limiting. This study was conducted to investigate the interactions between dietary ractopamine and betaine on growth and carcass characteristics in restrictively fed [31.0MJ digestible energy (DE)/day for 14 days followed by 36.8MJDE/day for 21 days] boars and gilts. Forty individually penned pigs (58.4kg) were allocated to a 2×2×2 factorial arrangement of treatments, with the respective factors being sex (gilt or boar), dietary betaine (0 and 1.5g/kg betaine) and dietary ractopamine (0 and 10ppm ractopamine) for 35 days. Over the first 14 days of the study when the restriction was greatest, daily gain was greater in pigs fed betaine (+8%, P=0.04) and in boars (+12%, P=0.005) but was not affected by ractopamine (P=0.18). Lean deposition was greater in pigs fed betaine (+5%, P=0.08) and in boars (+6%, P=0.006) but was not affected by ractopamine (P=0.57). However, there was an interaction (P=0.03) between ractopamine and sex such that ractopamine increased lean deposition in gilts but not boars. Thus, betaine and ractopamine had additive effects on lean mass in gilts (+5.1kg) but not boars. Fat deposition was less in pigs fed ractopamine (–8%, P=0.05) and in boars (–17%, P<0.001) but was not affected by betaine (P=0.81). However, there was an interaction (P=0.04) between dietary ractopamine and sex such that ractopamine decreased fat deposition in gilts (–14%) but not boars. In conclusion, dietary betaine and ractopamine may have additive effects on lean deposition and improve body composition in gilts but responses in boars are more equivocal. |
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